In the art of operating superconductor magnets, current is initially supplied from an external source to coils of the magnet (cooled below their critical temperature) until the desired level of operation is achieved. During this charging, a persistent switch across the magnet is maintained at a condition such that it exhibits a high resistance. When the desired current flow is reached in the magnet, the condition of the persistent switch is changed so as to exhibit substantially zero resistance so that the magnet current is completely shunted therethrough. At this point, the source can be turned off and/or disconnected using a mechanical switch or a disconnect of the type shown and described in U.S. Pat. No. 4,544,979. Numerous persistent switches are known in the art, and are typified by those of U.S. Pat. Nos. 4,164,777 issued to G. Kneip, Jr., et al., on Aug. 14, 1979, and 4,586,017 issued to E. Laskaris, et al., on Apr. 29, 1986. The persistent switches are then used to discharge energy stored in the magnet when operation of the magnet is to be intentionally stopped by changing the switch back to the high resistance state and routing the magnet's current through an energy absorbing device of some type.
There are types of superconductor magnet operation where the direction of current flow through the magnet needs to be reversed for the particular application of the magnet. To date, this reversal has been accomplished by mechanical or electro-mechanical switches (see FIG. 1) or by using expensive bi-polar power supplies. Electro-mechanical switches have traditionally been preferred for economic reasons. Due to the large currents flowing in the magnet, these switches must be structured to deal with these currents and the energy that can be stored in the magnet. These switches, as such, have moving components, heavy duty contacts and occupy considerable space. The making and breaking of high current contacts entailed in the operation of these switches render them prone to mechanical problems, particularly when operated frequently. In addition, since the power leads to the superconducting magnet must be physically opened during the reversing process using these switches, there are serious operator safety concerns as potentially fatal high voltages can occur. One should note that these current reversing devices have been required in addition to the persistent switch in a given magnet system.
In view of the state-of-the-art in superconducting magnet current switching, it is an object of the present invention to provide a switching system for reversing current flow in a magnet without the use of mechanical components.
It is another object of the present invention to provide a compact and non-mechanical switching system for use in reversing current flow to superconducting magnets and other high current devices.
It is a further object of the present invention to provide a superconducting switch for use in reversing the direction of current flow in a high current device.
An additional object of the present invention is to provide a superconducting switch useful for both reversing current flow and functioning as a persistent switch for superconducting magnets and the like.
These and other objects of the present invention will become apparent upon a consideration of the drawings identified below, and the full description thereof.